1. Field of the Invention
The present invention relates to imaging systems. More specifically, the present invention relates to infrared imaging systems and systems and methods for stabilizing same with respect to vibration.
2. Description of the Related Art
Imaging systems are widely used for numerous applications from navigation and guidance to astronomy. Infrared imaging systems allow for objects to be detected in low light level conditions that would not otherwise be detectable by the human eye. For this reason, numerous military systems have been supplemented in forward-looking infrared (FLIR) imaging systems.
Both FLIR and visible imaging systems suffer from image jitter due to vibration. Previously, imaging systems (particularly FLIR) used mechanical means to maintain the line-of-sight (LOS) stable. A common technique consisted of an inner gimbal, which, in essence, isolated the LOS from platform vibration that normally affected the outer gimbal. In general, airborne gimbaled systems are subjected to angular vibration inputs that result in residual servo errors. This servo error represents the deviation of the gimbal position from the pointing position. If left uncorrected, this error results in high frequency motion of the line-of-sight and degradation of the image. Hence, this method is not only limited as a solution, but it is costly and adds weight and size to the sensor, making this approach incompatible with many airborne applications.
Another technique utilizes a motion-compensating mirror built into the telescope to dynamically adjust the LOS. However, as with the previous method, this technique also increases sensor cost, weight and size. In addition, this system is difficult to implement as the mirror is fragile and requires a sophisticated control system. Further, the system performs poorly in that it creates an unsatisfactory rolling appearance to the operator.
A third method, purely electronic, uses memory to store the complete field of video and the corresponding vibration profile, which contains the LOS motion information. During read out to a monitor, the output video is stretched and compressed based on the recorded profile resulting in a stable LOS.
In addition to the memory necessary to store all the information required for post processing, this method has the disadvantage that any intermediate processing (e.g. target tracking) is performed on the image prior to stabilization. This results in performance degradation. In addition, the imagery is not available for tracking.
Hence, a need exists in the art for small, lightweight, effective yet inexpensive system or technique for compensating for jitter in imaging systems mounted on platforms that are subject to vibration and mechanical motion.
The need in the art is addressed by the image stabilization system and method of the present invention. The inventive system includes an image sampling circuit mounted on a platform for sampling an image in response to timing control signals and outputting a plurality of imaging signals in response thereto. An azimuth resolver detects vibration of the platform and providing a signal in response thereto. A microprocessor adjusts the timing control signals to cause the image sampling circuit to sample the image and thereby compensate for an effect of vibration on the imaging signals.
In the illustrative embodiment, the microprocessor includes software for compensating for vibration that causes image offset, compressed images, expanded images, and compression and expansion within a single field.
The present invention provides image stabilization in a purely electronic manner without the need for any moving parts that would typically require control hardware and a significant amount of space. In addition, since LOS motion compensation takes place as the image is being sampled, this method eliminates the need for the large amounts of memory required to store a field of video as well as LOS information for post processing.
The present invention may also offer improvements in system performance by providing the stabilized image to the autotracker thus minimizing track jitter and video latency.